It is often necessary to monitor the location and movement of materials within a distribution center or manufacturing facility. One method of tracking the materials is to attach a wireless communication device, such as a radio frequency identification (RFID) transponder or other identification device, to an article of manufacture including any type of physical device or container that houses materials. This application refers to this physical device or article of manufacture as a container for brevity sake only.
By way of example, a liquid container such as a barrel or keg may include an identification device indicative of the liquid contained inside. A transmission device, such as an interrogation reader or transmitter, having an antenna device, is able to send information remotely through electronic signals. Such transmission device is placed throughout the distribution or manufacturing facility to receive signals transmitted from wireless communication devices. The signals are then passed to a central control system that monitors and records the applicable information. The central control system can also send information to its interrogation readers to send to the transponders for response and/or to be stored in the transponder's memory.
The information communicated by the containers in the system to the interrogation readers may be used for a number of reasons. For example, a statistical analysis may be made of the materials to maintain an accurate inventories, production flow rates, and other production standards. Additionally, the identification devices may include specific information about the materials housed within the containers, including date of manufacture, place of manufacture, type of product within the container, temperature of the container and ambient air, temperature of the contents of the container, pressure of the container, etc.
The wireless communication device must have some type of antenna arrangement to communicate information about the containers to the interrogation readers. It is generally known for wireless communication devices to include an antenna. It is often a problem for many wireless communication devices to provide antennas, especially if the wireless communication device is small or is required to be placed in a contained area. The length of the antenna must be tailored to the specific frequency at which the wireless communication device is designed to operate. For low frequencies in the MHz range or lower, an antenna may have to be several inches long to several feet long. The antenna may have to be several inches long for higher frequencies, to allow for successful communication at the desired operating frequency.
Additionally, the antenna must either be packaged inside the wireless communication packaging that houses the wireless communication device, or located external to the wireless communication device. External positioning of the antenna to the wireless communication device provides several other challenges when placing the wireless communication device in a confined area, such as in a container. The antenna may have additional problems radiating energy effectively if the antenna is contained internal to a device, such as a container.
A beer keg is one example of a container that one may wish to attach a wireless communication device. A beer keg has a substantially cylindrical shape with a smooth, uniform outer wall. There are no extensions or areas for effectively attaching the wireless communication device. Even if the wireless communication device can be attached to the keg, additional problems in packaging and unaltered communication exists when including an antenna for the wireless communication device as described above.
Some containers have a natural slot as a characteristic of their manufacture. A slot may be formed by edges of a conductive material coming together in close proximity forming a gap of air between the edges. A slot may also be formed by cutting out or removing material from a conductive surface to form an open or hollow area of free space or air. A slot could be formed by a curl of a cylinder or other surface to form a rim, whereby a slot is created by the gap between the end of the curl and the surface.
For example, a beer keg is made out of a metal material that has an outer wall with a curled end to form a rim. The keg rim is used for handling and movement of the keg. The curled portion of the rim bends inward towards the outer wall, leaving a small gap between the edge of the rim and outer wall. This small gap forms a slot that extends circularly around the keg, and can be used to provide a slot antenna for the wireless communication device. The wireless communication device can be designed to provide electronic connectivity to the slot when installed, so that the slot can be used to provide the effect of an antenna. Since the slot of the container may be several feet long, using the slot for the antenna may be advantageous for communication at lower frequencies where providing an antenna of sufficient length for communication at the desired frequency is problematic.
Therefore, it is advantageous to use the slot of a container to provide an effective antenna for a wireless communication device. In the parent application of the present invention, use of the slot was explored at length. However, it has been discovered that there may be occasions when it is desirable to change the radiation pattern of the slot antenna such that it has better omni-directional receive and transmit capabilities. Further, there may, on occasions, be a need to change the operating frequency of the slot antenna such that the wireless communication devices operates at multiple frequencies.